The present invention relates to a system for crushing and discharging a powder and granular material that has become caked in a silo and incapable of being discharged by gravity flow.
Among tanks for storing powder and granular materials, grain silos are generally formed from concrete or iron plates. For example, an iron plate silo that has an inner diameter of 10 m and a height of 38 m can store up to 1,800 tons of grain.
With a view to storing grain in a stable state, it is desirable to lower the temperature and humidity in the silo. However, since no equipment for such purpose is available in general, it is a common practice to move the grain in the silo in quantities properly determined according to experiences, thereby preventing the grain from caking in the silo. In this case, however, the grain may cake if the interval of time at which the grain is moved is not properly determined and careful consideration is not given to the grain size of the grain and the amounts of water and oil retained therein.
It is known that grain causes a rise in the temperature thereof by its own respiration and the multiplication of microbes and this may invite an exothermic accident. The rise in the temperature of the grain also leads to caking. In addition, since grain is combustible and contains a large amount of dust, it involves the danger of dust explosion and must be kept out of fire and sparks. Since grain is a food material, it must also be kept out of any contaminative substance.
In general, grain that is to be stored in a silo is fed therein from the ceiling and discharged from an outlet in the bottom by gravity flow. If the grain has become caked in the silo, it cannot be discharged by gravity flow any longer and must be crushed in order to feed it out of the silo.
For this purpose, a manhole of about 600 mm is generally provided in the ceiling of the silo. When the grain in the silo has become caked and needs crushing, a crushing operation is conducted by use of the manhole. In the crushing operation, a boring machine is first installed on the rooftop of the silo, and then a rod is lowered through the manhole to bore a through-hole for discharge which extends from the top of the caked grain to the lowermost end. Thereafter, a special wire is passed through the hole to enlarge it, and then an operator goes down onto the caked grain and cuts it successively from the periphery of the through-hole with a coal pick hammer or other similar tool, thereby crushing and discharging the caked grain.
However, since the strength of the ceiling of the silo is limited and no lifting equipment is available, it is impossible to install a large-sized machine on the rooftop of the silo. For this reason, it is only possible to adopt a boring machine or the like, which is classified as a relatively small-sized machine. In some cases, there is a shed above the rooftop of the silo and the crushing operation must be carried out inside the shed. In such cases, since the building is not sufficiently high and a large number of installations, for example, conveyor and piping, are disposed on the rooftop of the silo, even the space required for scaffolding cannot be ensured satisfactorily and it is also difficult to bring a boring machine onto the rooftop of the silo and move it there sidewardly.
In addition, the diameter of the hole that is drilled by the boring machine is so small that the hole needs to be enlarged by means of a special wire. Since the hole is likely to curve, the silo wall may be damaged and there is another problem that the grain may be burned by the frictional heat that is generated between the machine cutter and the silo wall.
Further, since the operator must enter the silo through the manhole provided in the ceiling and crush the caked grain by a manual operation, the burden on the operator is considerably heavy and the working environment is bad. More specifically, a silo that is stored with grain may be short of oxygen, and since the operator must enter the silo through a manhole provided in the ceiling that is as high as 35 m, various problems arise from the viewpoint of safety.
As has been stated above, the cake crushing operation in the silo involves fears that the inside of the silo may be short of oxygen, that the operator may slip and fall during the crushing operation, that the operator may be buried alive in the grain collapsed, that a fire may start in the silo by an unexpected accident, and that a cardiopulmonary disorder may be caused by the dust resulting from the crushing of the caked grain. It is therefore necessary to take a measure to prevent the operator from slipping down, instruct the operator to wear a dust-proof mask, and effect ventilation. In addition, since the crushing operation is carried out by human power, the operating efficiency is low, and if the operation procedure is carried out inappropriately, the caked grain may collapse in the form of a huge heap and destroy the substructure of the silo.